Use multiple threads to import.

- For now everything imports multithreaded by default (should work I guess, let's test).
- Controllable per importer

Early test benchmark. 64 large textures (importing as lossless, _not_ as vram) on a mobile i7, 12 threads:
Importing goes down from 46 to 7 seconds.

For VRAM I will change the logic to use a compressing thread in a subsequent PR, as well as implementing Betsy.

1 files changed, 2 insertions, 0 deletions

diff --git a/editor/import/resource_importer_scene.h b/editor/import/resource_importer_scene.h
index 6c6af57c4c..00039f2ac6 100644
--- a/editor/import/resource_importer_scene.h
+++ b/editor/import/resource_importer_scene.h
@@ -173,6 +173,8 @@ public:
 	virtual bool has_advanced_options() const override;
 	virtual void show_advanced_options(const String &p_path) override;
 
+	virtual bool can_import_threaded() const override { return false; }
+
 	ResourceImporterScene();
 };